Osteoarthritis (OA) is a painful and debilitating disease of the synovial joints, affecting an estimated 12% of the total United States population 25-74 years of age. The prevalence of this disease increases significantly with age, with radiographic evidence observed in over 70% of the population over age 65. OA research is important, considering the extensive impact and public health consequences of this disease. The etiology of OA is not fully understood, and there exist no disease-modifying therapies. OA is distinctively characterized by the progressive, degenerative changes in the morphology, composition, and mechanical properties of articular cartilage, indicating that the normal balance of metabolic activities in chondrocytes, the cellular element that makes and maintains all cartilage, has been severely disrupted. While the relationships between the biochemical and biomechanical events involved in this pathology are not yet known, it is now evident that mechanical factors play a critical role in the sequence of events leading to the metabolic imbalance of cartilage in OA. The over-riding objective of this study is to deconstruct mechanosensitive signaling in primary chondrocytes to provide better understanding of a basic mechanism of enormous relevance, and also to provide critical insight to enhance more rational therapies of joint-loading-induced injuries including OA. We have made an exciting discovery of expression of PIEZO mechanosensitive channels in chondrocytes, which appear functional in response to mechanical loading. Thus, the Specific Aims of this grant are: (1) to examine the role of PIEZO channels in controlling the anabolic and catabolic response to physiologic and excessive mechanical loading using an organotypic preparation of cartilage. (2) In a mouse post-injury arthritis model, to apply the Piezo antagonist GsMTx4 to the affected joint as a means of preventing chondrocyte-mediated joint degeneration. Aim 1 will be in a porcine model and take advantage of the spider toxin GsMTx4, which blocks Piezo channels. Aim 2 will take advantage of a post-traumatic arthritis model that we have adopted to mice, with a read-out of gait change and joint histology. Based on our exciting discovery, addressing these Aims will increase our insights into OA pathophysiology in a non-incremental way, and directly guide us towards new specific therapies.